1. Field of the Invention
The present invention relates to a resin composition having excellent moldability and gas shut-off property, and to a multi-layer container having an oxygen-absorbing layer of this resin composition.
2. Prior Art
As packaging containers, there have heretofore been used metal cans, glass bottles and a variety of plastic containers accompanied, however, by problems of disintegration of the contents and loss of flavor due to oxygen remaining in the containers and due to oxygen that enters permeating through the container walls.
In the case of the metal cans and glass bottles, quite no oxygen enters permeating through the containers walls, and only oxygen remaining in the containers could cause a problem. In the case of the plastic containers, however, oxygen enters permeating through the container walls to a degree that is no longer negligible arousing a problem from the standpoint of preserving the contents.
In order to prevent this, the plastic containers have been produced having container walls of a multi-layer structure containing at least a layer of a resin having oxygen-blocking property, such as an ethylene/vinyl alcohol copolymer.
A deoxidizing agent has long been used for removing oxygen in the containers. Japanese Examined Patent Publication (Kokoku) No. 1824/1987 discloses an invention using the deoxidizing agent for the container walls, according to which a multi-layer structure for packaging comprises, laminated one upon the other, a layer blended with the deoxidizing agent containing, as a chief agent, a reducing material such as iron powder or the like in the resin having oxygen-permeating property, and a layer having an oxygen gas shut-off property.
Japanese Examined Patent Publication (Kokoku) No. 60826/1992 proposed by the present inventors discloses a plastic multi-layer container comprising a laminated structure of:                an intermediate layer of a resin composition of a gas-barrier thermoplastic resin having an oxygen permeation coefficient at 20° C. and 0% RH of not larger than 10−12 cc·cm/cm2·sec·cmHg and a water-absorbing amount at 20° C. and 100% RH of not smaller than 0.5% blended with an organometal complex of a transition metal; and        layers of a moisture-resistant thermoplastic resin formed on both sides of the intermediate layer.        
Japanese Patent No. 2,991,437 teaches a barrier wall for packaging including a composition of a polymer having oxygen-trapping property or including a layer of this composition, wherein the composition traps oxygen as an organic oxidizing component is oxidized with a metallic catalyst, the organic component that can be oxidized being a polyamide and, particularly, a polyamide containing a xylylene group.
A method of blending a resin with an oxygen-absorbing agent such as an iron powder to use it as a wall of the packaging material is satisfactory from the standpoint of large oxygen-absorbing ability but cannot be used in the field of packages where transparency is required since it causes the resin to be tinted in a specific hue.
On the other hand, an oxygen-absorbing resin composition containing a catalyst of the type of a transition metal is advantageous since it can be used even for the packaging containers that are substantially transparent accompanied, however, by such a defect that a base resin blended with the catalyst of the type of a transition metal is deteriorated upon the oxidation permitting the permeation of oxygen through the container wall to increase with the passage of time and, further, causing the strength of the container to decrease.